Mechanism for casting metals in investment material



G. A. YA NTIS 2,171,778

MECHANISM FOR CASTING METALS IN INVESTMENT MATERIAL Sept. 5, 1939.

Filed April 27, 1938 I 4 Sheets-Sheet 1 INVENTOR 6e 1? Yamis ATTORN EY G. A. YANTIS 2,171,778

MECHANISM FOR CASTING METALS IN INVESTMENT MATERIAL Sept. 5, 1939.

4 Sheets-Sheet 2 I Filed April 27. 1938 j NVENTOR I 560%?6 fl. Yaw/D5 ATTORNEY Sept. 5, 1939. YANTls 2,171,778

MECHANISM FOR CASTING METALS IN INVESTMENT MATERIAL Filed April 27, 1938 4 Sheets-Sheet 3 5 ATTORNEY Patented Sept. 5, 1-939 UNITED STATES MECHANISM FOR CASTING METALS IN INVESTMENT MATERIAL George A. Yantis, Elma, Wash. Application April 27, 1938, Serial No. 204,61!

13 Claims.

My invention relates to a mechanism for carrying out the process of casting metals in investment material. More particularly, my invention relates to a device which will control the conditions of casting to carry out a process of casting metals in investment material so that the shrinking of the metal upon cooling will not provide a molded product of a size different from that desired.

My invention will be described as applied to dental castings, as inlays, crowns, partial dentures etc. although the invention is not to be limited to any such specific application, but is to be coextensive to all applications involving like condi- 15 tions.

Heretofore great diificulty has been experienced in the production of accurate castings. A perfect impression in wax, of a cavity in a tooth may be obtained, but, because of the shrinkage of the gold from the molten to the solid state, difliculty in accurately reproducing the wax mold of the cavity into gold is encountered.

A primary object of my invention is to provide the mechanism for carrying out a method of casting the metals so that the cast product will be of the desired size.

Dental gold is usually alloyed with other metals to give it required hardness and wearing qualities. When this dental gold is melted or is heated in the presence of air, as for tempering or soldering, the metals which are alloyed with the gold will oxidize, forming a scum on the outside of the metal. This oxidation tends to retard free flow of the metal, leaves the casting or heat treated part dirty and coated on the outside so that it must be cleaned by a pickling process using acid, and further changes the percentages of the different metals in the alloy. In accordance with common practice this oxidizing of the metal and the objectionable results of such oxidation are overcome, to a certain extent but not entirely, by the use of fluxes which prevent some of the oxidation and make the metal flow more freely when molten and which facilitate soldering of the metal.

In accordance with this invention I provide for heating and melting the metal in the presence of a gas which contains no free oxygen and is herein termed an inert gas thus completely preventing oxidation, insuring a product which is always clean and does not need to be pickled or cleaned, insuring a product which flows freely, and tending to produce more'accurate work due to the fact that there is no change in the percentages of metals in the alloy and no coating of oxidized metal on the exterior of the finished work. Also excluding the air and casting in the presence of an inert gas makes it possible to fuse molten metal to solid metal and thus obviates the necessity of soldering diiferent pieces together' after casting. This saves time and labor. 5

In casting metals in investment material the expansion of a given investment material will vary in proportion to the temperature, it being common knowledge that someinvestment materials have a difierent coeflicient of expansion than others. Also the molten metal will have a certain amount of shrinkage upon cooling. In dental casting it may be desirable to allow a slight amount of clearance for cement or to make a part, as a dental crown which is to fit over a tooth, slightly oversize, or to make a part which is to fit into a cavity, such as an inlay, slightly undersize to insure proper clearance. To accomplish this it is desirable to be able to determine very accurately the temperature of the investment in which the casting is being made. It is an object of my invention to provide a combined furnace and casting machine having pyrometer means for accurately indicating the temperature of the investment material and having variable 25 heat means for heating the investment material to any desired predetermined temperature, thereby making it possible to have the investment material at precisely the correct temperature for the casting of the metal in each individual case and in this way insuring the production of better castings.

Another object of my invention is to provide a combined furnace and casting machine in which the metal is electrically melted, thus avoiding the use of oxidizing torch flames on the metal and keeping the metal clean and pure.

Another object of the invention is to provide a furnace adapted for the reception of an investment ring containing investment material and having a crucible movable into and out of registration with the end portion of said investment ring and adapted to deliver molten metal directly into a mold cavity in the investment material in said ring.

Another object of the invention is to provide a combined furnace and casting machine having means for admitting an inert gas under pressure into the crucible where the gold or like metal isbeing melted to drive out the air prior to the 50 melting of the metal and to help force the metal into the mold after it is melted.

Another object of this invention is to provide a combined furnace and casting machine in which both the furnace portion, and the crucible portion are capable of independent use for heat treating or tempering metal parts or for baking porcelain parts.

The above mentioned general objects of my invention, together with others inherent in the same, are attained by the devices illustrated in the following drawings, the same being preferred exemplary forms of embodiment of my invention, throughout which drawings like reference numerals indicate like parts:

Figure 1 is a verticalsectional view, with parts in elevation of two furnaces of different size and a'crucible means constructed in accordance with this invention, showing investment rings of different size, each with investment material therein disposed within said furnaces and showing a crucible movable into operative relation with respect to either furnace and adapted to deliver molten metal into a mold cavity in the investment material in the selected furnace;

Fig. 2 is a vertical sectional view of a modified form of this invention;

Fig. 3 is a sectional view substantially on broken line 33 of Fig. 2;

Fig. 4 is a vertical sectional view of another modified form of the invention;

Fig. 5 is a view partly in elevation and partly in section substantially on broken line 5- -5 of Fig. 4;

Fig. 6 is a fragmentary sectional view on a larger scale than Fig. 4,.showing a valve device embodied in the apparatus shown in Fig. 4;

Fig. 7 is a detached edge view of a door applicable to the retort shown in Fig. 4;

Fig. 8 is a sectional view of another modified form of the invention;

Fig. 9 is a sectional v1ew of still another modified form of the invention;

Fig. 10 is a plan view of a base member adapted to be used in preparing an investment within an investment ring;

Fig. 11 is a sectional view of said base membe substantially on broken line of Fig. 10;

Fig. 12 is a fragmentary plan view of the under side of a top plate member;

Fig. 13 is a diametrical sectional view of said top plate member in inverted position and in operative relation to an investment ring, a fragment ofwhich is shown;

Fig. 14 is a plan view of the upper side of a sprue wire holder;

Fig. 15 is a sectional view of a modified form of sprue wire holder;

Fig. 16 is a detached elevation of a U shaped sprue wire;

Fig. 17 is an end view of an investment ring with positioning notches therein;

Fig. 18 is a fragmentary side view of said investment ring; and

Fig. 19 is an exploded sectional view of a table.

Referring to Figure 1 of the drawings, 20 designates a base and 2| and 22 two furnaces of refractory material mounted on said base at equal axial distances from an upright tubular post 23 on the base. The refractory furnaces 2| and 22 each have a lining 24 of heat insulating material provided with grooves 25 within which electric heating coils 26 are disposed. I have shown an investment ring 21, containing investment material 28, disposed within the lining 24 of each furnace. Also I have shown in the investment material 28 in each ring 21,

a cavity 3| which is adapted to receive molten metal. A pyrometer member 30 having the usual pyrometer devices therein extends from the base 28 upwardly through the bottom of the furnace housings 2| and 22 and lining 24 and has the tip portion 1 thereof positioned'in contact with the investment material 28. Connecting wires 32 and 33 connect the pyrometer member 38 of the respective furnaces 2| and 22 with terminals 34 and 35, which are adapted to be engaged by a pivoted contact arm 39. The arm 39 is connected by a wire 36 with dial and pointer means 31 on which the temperature of the investment material in either furnace maybe registered. Tension springs 38 yieldingly support the pyrometer members 30 in such a manner as to permit said members to be pushed downwardly by contact with the investment material, thus insuring firm contact between the pyrometers and the investment material. or other. yielding means may be used in place of springs 38.'

A cover member 40- of heat refractory material is connected by hinge means 48' with the smaller furnace 2| and is adapted to close the opening in the top end portion of the said fur- .nace 2| whensaid furnace is not in use. A

fragment of this cover member 23 is shown in an open position in Fig. 1. A separable and removable cover member 4| is provided for the larger furnace 22. Either type of cover could be used on any types of furnace described.

Preferably the heating coils 26 in the furnaces 2| and 22 are respectively connected by suitable conductor means shown diagrammatically by 42 and 43 with multiple heat switches 44 and 45.

. These devices provide for varying the amount of heat supplied to the furnaces, but, as said devices are of old and well known form, they are not herein shown and described in, detail. Any other type of heat control can be used in the place of the switches or in conjunction with them.

Extending upwardly from the base 20 between the two furnaces 2| and 22 is the tubular support .23 upon which a bracket arm 46 is slidably mounted for longitudinal and angular movement. A screw 41 serves to lock the bracket arm 46 in any desired vertical or angular position on the upright support 23. An extension bracket 48 is rotatably disposed within the bracket arm 46 and a screw 50 prevents disengagement of .arm 46 and bracket 48. A crucible housing 5|, of refractory material, is secured to the extenthe bottom portion thereof upwardly, and in this recess is a lining 52 of porcelain or like material within which suitable electricheating element means 53 is embedded. A crucible 54, preferably of semi-cylindrical shape, is mounted within the lining 52 on pivot means 55. This pivot means 55 is positioned near the open upper end portion of the crucible so that said crucible will tend to hang by gravity in the position shown in Figure 1. A plan view of a crucible similar to the one shown in Figure 1 is shown in Fig. 3 and the parts therefore correspondingly numbered. The crucible 54 is externally provided adjacent the open top portion thereof and at substantially right angles to the axis of the pivot means 55 with an outwardly projecting vane 56 which is positioned within an arcuate groove 51 in the wall of the lining 52. A pas- Friction means sageway '58 for inert gas extends downwardly in the crucible housing SI and is thence curved inwardly and upwardly in substantially J shape and extends through the lining in substantially the manner shown in Figure 1 so that a blast of fluid, such as inert gas, may be discharged into the crucible chamber and against the vane 56 to angularly move the crucible on the pivots i5 and dump the contents thereof.

Preferably a flexible tubular conduit 60 is connected with a suitable source of supply of inert gas, not shown, and extends upwardly through the tubular post 23 and thence to pipe means 6| which communicates with the passageway 58 so that inert gas under pressure may be supplied to the passageway 58. A valve 62 is provided for controlling the flow of this inert gas.

Suitable electrical conductor means 63 prefer ably extends from a multiple heat switch 64 on the base 20 to the electric heating element 53 in the crucible lining whereby a variable or controlled heat may be provided for the crucible. A pyrometer 65 is provided in the crucible housing 5| and is connected by a wire 66 with a con tact member 61 which is adapted to be engaged by the contact arm 39 so that the heat of the crucible may be read on the dial and pointer means 31, the wire 61 passing through tubular post 23.

The showing of the several pyrometers and means for reading the temperatures registered therby is somewhat diagrammatic, it being understood that standard pyrometer mechanism is used and that the arrangement is such as to makeit possible to selectively read the temperature registered by any pyrometer member when the contact arm 39 is placed on the contact member 34, 35 or 61 connected with that pyrometer member.

In Figs. 10 to 18 inclusive I show certain preferred types of investment rings 21 and devices used in connection therewith for facilitating the handling of the investment preparatory to castin'g. To insure the proper centering of the investment rings 21 within the furnaces I provide a plurality of V shaped notches 68 in both ends of the rings 21, see Figs. 17 and 18. I have shown four notches 68 in each end of each ring 21 but it will be understood that this centering can be accomplished with two of such notches 68, provided they are not diametrically opposite to each other, or with any desired number of said notches more than two. Preferably the notches 58 are in duplicate in the two ends of the rings 2'! so that the rings 2 are reversible.

For usein connection with the notched investment rings in preparing an investment, I preferably provide a top plate 10, Figs. 12 and 13, and

a base plate ii, Figs. 10 and 11. The base plate 11 preferably is of inverted cup shape as shown in Fig. 11 and has a centrally positioned pin 12 frictionally held in the plate and manually adjustable longitudinally, to form, in the investment material, an opening of correct size to receivethe pyrometer 30. Obviously the top and bottom plates may be duplicates with a central hole the size of the hole 15 in plate l and a bushing, not shown, may be used on pin 12 to fit within hole 75 which is of larger diameter than pin 12. The base plate H has a plurality of radially extending ribs or tongues 13 of inverted V shape on the top side thereof and the top plate ill has a plurality of correspondingly positioned ribs or tongues M. The topplate ill also has a central opening I for the reception of a shank U shaped wires 80 embedded in-the wax impressions or molds 82 to be supported and the curved portions thereof inserted in the slots 18. The

slots 18 may be arranged as shown in Fig. 14 and are preferably divergent so that several sprue members 80 may be supported in diverging relation by one sprue wire holder 11.

Fig. shows a modified form of sprue member support 8| which is similar to the sprue member support shown in Figs. 13 and 14, except that the centering shank l6 thereof is omitted and the said sprue member support 8i depends entirely on vacuum cup action to hold it in place. When a sprue member support 8| of the form shown in Fig. 15 is to be employed, the top plate, not shown, with which it is to be used will be without any central perforation and will be of glass or porcelain or like material to which a vacuum cup will adhere.

In setting up an investment for casting, the topplate 10 is preferably supported horizontally in an inverted position, as shown in Fig. 13. The wax impression or mold 82, Fig. 13, having been properly prepared is supported on one or more suitable sprue wires 80, which are held in the slots 18 in the sprue wire support 11 and the ring 21 fit over the tongues 14 on the plate 10 and the ring 21 is properly positioned. The investment ring 21 is then filled with plastic investment material so as to properly embed the wax impression 82 in the investment. The base member 'H is then inverted, placed on the ring 21 and adjusted so as to properly center it and the pin 72 is then pressed into the soft investment material a desired distance to make a hole for the future entrance of a pyrometer tip. After the investment material has hardened sufficiently, the entire assembly comprising the ring 21 and the top member 70 and the base H may be turned right side up, the top member ill together with the sprue wire holder 11 and sprue wire 80 removed, and the investment ring 21 separated from the base II and made ready for the casting operation.

The V shaped ribs 13 on the base plate member II will leave V shaped radial grooves in the investment material in line with the notches 68 in the ends of the investment rings 21 and these grooves will fit over correspondingly positioned V shaped ribs 83 in the bottom portion of the furnaces when the rings 21 with investment therein are placed in the furnaces, thus insuring proper positioning of the rings 21 in the furnaces. Preferably the height of the ribs 83 in the bottomportion of the furnaces is greater than the depth of the notches 88 in the end of the investment rings and the corresponding notches in the adjacent investment material so that the investment ring and investment material will be spaced 'a short distance above the bottom of the furnace to provide for a free escape of air which is driven out of the crucible and furnace when the inert gas under pressure is admitted. This air is driven off through the porous investment material and escapes up past the investment ring and out through a suitable opening between the top portion of the furnace housing and the bottom portion of the crucible housingil. Preferably the crucible lining 52 extends downwardly far enough so that it engages with the investment material in the adjacent ring 21 and forms a seal to retard the escape of inert gases at this location. It is to be noted that the sprue wire holder 11 will al-- "ing an ungrooved ring of investment material'to make sealing contactwith the end portion of the lining 52. This is true both for the smaller investment rings, as shown in the furnace 2| and the larger rings, as shown in the furnace 22 in Fig. 1. It is to be noted that the investment ring '21 shown in Fig. 13 is a ring of small size while the ring 21 shown in Figs. 17 and 18 is of intermediate size and the ring 21 shown in the furnace 22 in Fig. l is of large size.

When the sprue wires are withdrawn from the investment material and wax impressions 82, they leave the wax impressions 82 in the investment material and leave one or more channels 85 through which molten metal may flow into the cavity which is left after said wax-impressions are melted out of the investment material.

The two furnaces 2| and 22 are positioned with their axes at equal distances from the center of the tubular post 23 so that the crucible assembly, which is angularly movable about the tubular post 23, will register correctly with either of said furnaces. Obviously only one furnace or more than two furnaces may be provided on the base 20 if dsired. After an investment has been properly prepared it is placed in one of the furnaces 2| or 22 and will be correctly centered therein by the radial ribs 83 in the furnace. An amount of gold alloy sufficient for the casting to be done is placed in the crucible 54. This insertion of the gold alloy may be easily accomplished by loosening the screw 50 and angularly moving the crucible assembly on the bracket extension 48 far enough to afford access to the interior thereof. At the time this is done the crucible assembly will be elevated on the tubular post 23 and preferably will be angularly positioned so that it will not be in registration with either furnace. After the metal, such. as gold alloy, which is to be melted has been placed in the crucible 54 the crucible assembly will be angularly moved on shank 48 back into the upto furnace 2| and will enter a short distance into lining 24 of furnace 22 when in casting position relative to furnace 22.

After a properly prepared investment has been placed in a furnace, the furnace is initially heated up to vaporize and evaporate the wax impression and leave a proper cavity in the investment and .to bring the investment up to proper temperature. This may be done either with the cover of the furnace closed or with the crucible assembly in place on top of the furnace. The pyrometer 38 will recordaccurately the temperature of the investment, thus making it possible to bring the investment up to any desired temperature to secure a desired expansion of the same.

After the crucible housing has been operatively positioned as respects the furnace being used, and preferably just before the heating of the metal to be melted begins, the valve 62 is opened a slight amount to admit just enough inert gas to drive out the air and fill the crucible chamber and cavities in the investment with inert gas. The

metal to be cast, such as gold alloy,.is thus heated.

up and melted in the presence of a gas free from oxygen so that no oxidizing thereof can take place. After the temperature of the crucible, as

indicated by pyrometer 65, has been raised sufficiently high to insure that the metal or alloy-is properly melted and ready for casting the operator quickly opens the valve 82 enough to dis- -charge a blast of inert gas through the passageway 58 and against the vane 56. This angularly moves the crucible 54 through an angle sufficient to dump the molten metal from the crucible into the spherical depression 84 in the top'portion of the investment. At the same time the pressure of inert gas within the crucible and above the investment rapidly rises and aids gravity by tending to drive the molten metal into the mold, thus insuring a perfect casting made under accurately controlled temperature and expansion conditions of the investment and in the absence of oxygen.

Proper casting temperature of the metal may be insured by a reading furnished bypyrometer 85, or a sight opening means of the form shown at I55, Fig. 8, may be provided to permit observation of the metal, or both the pyrometer and the sight opening may be used.

Fig. 2 shows mechanism which differs somewhat from that in Figure 1, but which provides for casting in the absence of oxygen and under the same accurately controlled temperature conditions. In Fig. 2 I show a furnace 86 similar to furnaces 2| and 22 and having correspondingly numbered parts. A crucible housing 81 is hinged to furnace 86 by hinge means 88. This hinge means is preferably capable of being easily disconnected, so that crucible housing 81 can be used interchangeably with furnaces of different size. Also detachment of crucible housing 81 makes it possible to use a door or cover plate on the furnace 86. A readily detachable fastening means 98 is provided substantially opposite the hinge means 88 to cooperate in securing the crucible housing to the furnace. The crucible housing 81 has a recess 9| in the bottom portion thereof and has a cylindrical passageway 92 extending from the top downwardly and intersecting said recess. A crucible lining member 93 is longitudinally movable in the recess 9| and has a shank 94 extending into the passageway 82. Devices for moving this crucible lining 93 are connected with the outer end portion of the shank 84. The means herein illustrated for accomplishing this movement comprises a rotatable hand wheel 95 retained in position and rotatably connected with the crucible housing 81 by split collar means 96 secured to the housing 81 and fitting into a groove 91 in the hand wheel 9 5.'

The hand wheel 95 is threaded onto a. shank 98 which is relatively rotatively secured by a split collar I00 and nut IM to the end portion of. the shank 94 so thatrotation of the hand wheel 95 will longitudinally move the lining 93 and parts 94 and 98 connected therewith. This provides for adjusting the lining member 93 to properly engage with the investment material in investment rings of difierent size. A position which the end of lining member 93 may occupy to engage with the investment material in a small ring is shown by dot and dash lines in Fig. 2. The lining member 93 has a crucible 54 pivotally mounted therein by pivot means 55 and adapted to be angularly moved to dump molten metal therefrom by a blast of inert gas under pressure discharged from a passageway 58 against a vane 56, all as previously described in connection with Fig. 1, in which corresponding parts are correspondingly numbered. The passageway 58 in Fig. 2 is formed entirely within the lining 93 and shank 94 and communicates with a similar passageway I02 in the shank 98. Passageway I02 is connected with conduit means I03 for the supply of inert gas under pressure, said conduit I03 having a valve I04. Aligned passageways I05 and I06 are provided in shanks 94 and 98 for the entrance therethrough of electric current supply wires to the heating means in the lining member 93.

The operation of the apparatus shown in Fig. 2 is similar to the operation of the apparatus disclosed in Figure 1, except that the crucible assembly is mounted and handled in a different manner and the lining member 93 which carries the crucible is adjustable to engage with investment in rings of varying size.

Figs. 4 to 6, inclusive, show a device in which the crucible assembly is pivotally mounted and the furnace is hinged to the crucible and the molten material is discharged by gravity in response to a change in angular position of both the crucible assembly and the furnace, which, at the same time, admits the gas.

Figs. 4-6 show a crucible housing I01 having a transverse tube I08 embedded therein near one end. The tube I08 is pivotally mounted on a horizontal tubular bearing member IIO which is supported in upright supports I II and also serves as a conduit for inert gas delivered thereto through conduit means II2 having a control valve II3 therein. The crucible housing I01 has a lining H4 therein which is recessed for the reception of a crucible I I5. The lining I I4 has electric heating means IIG embedded therein. Preferably the crucible I I5 is removable through the open end portion of the lining and the rear edge portion of said crucible is engaged behind a hook like retaining member I I1 in the lining II 4 when said crucible is operatively positioned within the lining II4.

A passageway II8 for the inlet of inert gas under pressure extends from the tube I08 to the chamber within the lining II4. A port I20 in the tube I08 registers with the passageway II8. Another port I 2I in the tubular bearing member H0 is positioned so that it may, register with the port I20 as shown in Fig. 6, or may be angularly ofiset as respects the port I20 as shown in Fig. 4, depending on the angular position occupied by the crucible housing 101, A perforation 122 of small size in theimember II0 'is positioned to reg ster with: the port- 120: inq he tube I08 when the crucible housing I01-is in a generally horizontal position, as shown in Fig. 4. The purpose of this small perforation I22 is to permit a small amount of inert. gas under pressure to flow into the chamber in lining II4 to driveout the-air and surround metal in the crucible during the melting process. A loose fit-of member H0 in tube I08 will accomplish the'same function. The purpose of the port I2I is to permit a free flow of inert gas under pressurefor driving the molten metal into the mold cavity as soon as said molten metal is discharged from the crucible by reason of the crucible housingI01 andfurnace, attached thereto, swinging from the horizontal position shown by full lines inFig; i to the vertical 'position shown by dot and dash lines.

A furnace I23 is connected with the crucible housing I01 in end to end relation withresp'ect thereto by hinge means I24-and adjustable securing means I25; The furnace I23 has a lining I26 provided with electric heating means I21 which is provided in the bottom portion as well as in the side portions of said lining. "An adjustable bottom plate I28 is providedin furnace I23 to adjustably support investment rings of different sizes in engagement with theinner' end portion of the crucible lining II4. This makes the casting deviceshown in Figs. 4 to 7 adaptable for the reception of rings of different sizes. The bottom plate I28 has a shank I30 thereon which is seated within a screw member I3I. The member I 3I is threaded into a fitting I32 which is secured to the furnace housing I23. A pyrometer mem- [ber 30 entersthrough the shank I30 and contacts the investment material 28 in which the casting is being made. The bottom plate I20 is preferably provided with ribs I33 similar to the ribs 83 described in connection with Figure 1 to center the investment ring and hold the investment material slightly spaced'from the plate I28, whereby air may escape more easily.

A latch member I34 is pivotally mounted on a non-rotatable cross bar. I 35 and has hook portions I36 adapted to engage with hookmeans I31 on the crucible housing, I 01 to hold the crucible housing in a horizontal or an inclined position. A stop pin I38 carried by the latch member I34 is adapted to engage with a fixed stop collar I39 on the bar I35 to m'aintainth'e latch'member I34 in a substantiallyhorizontal position, whereby it will automatically engage with thehook means I31 when thecrucible housing is swung'upwardly from a verticaltoward a horizontal-position."

In the operation of the device shown in Fig. 4 the gold alloy or like metal ismelted in the crucible with the parts'in theposition shown by full lines. Before starting to heat-"this metal the valve I I3 is opened and inert gas turned on. Enough of this gas will."enter throughi'perforation I22 to driveout the air *anqinsure that the heating and'melting is don'e'in "the presence of the inert gas. When the metjalltobecast'is properly melted the latch membe'r I34 is re'- leased. This causes the crucible ho sing" I01 drive the molten metal into the molds The furnace housing :I'23may-be swung' downmentarily by dot and dash lines in Fig. 4 to afford easy access to the interior of both the furnace and the crucible. Also the crucible may be used for heat treating or tempering gold or like parts and when it is to be so used a separate closure member I40, Fig. 7, having pin means I4I projecting perpendicularly therefrom is applied to the open end portion of the crucible by inserting the pin means I4I in holes I42, which are provided in the crucible housing I01. One of these holes is shown by broken lines in Fig. 4. This closure member is thus supported so that it may be positioned against the end of the lining II4 to completely close the opening to the crucible chamber or it may be moved outwardly therefrom to allow the escape of some heat. This provides a heat control means which is useful where it is desired to permit slow cooling of a part. This makes it possible to use the crucible for baking porcelain parts, or for heat treating metal or other parts. The same door I40 can be used in any other furnace shown here also.

Fig. 8 shows a modified form of the invention in which a furnace I43 and crucible I 44 are both mounted on hinge means I45 for swinging movement through an angle of approximately ninety degrees and in which the crucible I44 is supported on an arm I46, which is slidable and angularly movable on a guide member I41. guide member I41 is rigidly connected with a separable base portion I 46 upon which the furnace I43 is mounted. The hinge I 45 connects the furnace base I48 with a base support I50. The furnace I43 has a lining I5I provided with electric heating coil means I52. An investment ring 21' with investment material therein is shown in the furnace I43. This investment ring 21' is plane and fiat and free from notches on the ends and the inner end portion of the crucible makes sealing contact with the end of this investment ring 21'.

Pyrometer means 30 is provided in the bottom portion of the furnace I43 to contact the investment material 28 and accurately register the temperature thereof. Preferably the furnace I43 is separately connected with the base portion I48 by plug means I53, whereby furnaces of different size may be plugged in on this same base and used in connection with the crucible portion I44. The electrical connections are also preferably made through the plug means I 53. If a large furnace is used in the place of furnace I43, an opening in the hinged door on the furnace would be made by removing a removable port in the door the size of the crucible housing I44, thereby allowing the crucible I44 to extend into the door and contact with the investment ring 21'. The remaining outer portion of the door would then close the space on the face of the furnace I43 around crucible I 44, which'would be smaller than the opening in furnace I43.

A suitable conduit I54 is connected with the chamber within the crucible housing I44 through which inert gas may be admitted and the crucible housing I44 is provided with a sight tube I55 through which the condition of the metal used for casting may be observed. Preferably a transparent disc I49 is provided at the outer end of the sight tube I55. A sight tube of this nature may be used with any of the furnaces here in disclosed.

In the operation of the device shown in Fig. 8, when an investment ring 21 is to be inserted in or removed from the furnace the crucible is withdrawn from the mouth of the furnace and anadmitted to drive out the air.

gularly moved to one side of the mouth of said furnace. Also the furnace is angularly moved counterclockwise on hinge I45 substantially ninety degrees from the position shown in Fig. 8, so that the mouth of the furnace is uppermost, thereby permitting easy insertion and removal of the investment ring. After the investment ring has been inserted, the furnace and crucible may be angularly moved back into the position shown in Fig. 8, the metal to be melted placed in the crucible and the crucible moved into the end of the furnace against the end of the investment. The investment material may then be heated to the desired degree, inert gas having been admitted through the tube 18. After the metal is melted and the desired temperature of the investment material obtained, the furnace and crucible are angularly moved counterclockwise from the position shown in Fig. 8 to discharge the molten metal by gravity into the cavity in the investment material. At .the same time a larger supply of inert gas will be admitted to help force the molten metal into the mold.

In Fig. 9 I have shown another modified form of my invention which is similar to the form shown in Fig. 8, except that the crucible is secured to the furnace door. In said Fig. 9, I56 is a furnace, which is pivotally mounted by horizontal pivot means I51 on a support I58. The furnace I56 has a lining I59 provided with electric heating coils I60 and has pyrometer means 30 in the bottom portion thereof. An investment ring 21' within the furnace I56 has investment material 28 therein. A furnace door I62 is pivotally secured to the furnace I 56 by hinge means I63 and has annular steps I64 on its inner side adapted to fit withininvestment rings 21 of different size, which are positioned within the furnace. The inner side of the door can be fiat in place of having the steps I64, if desired. I65 is a crucible housing integral with or secured to the furnace door I62 and positioned on the outer side of said door I 62 and adapted to communicate with the inside of the furnace. The crucible I65 has a, sight tube I66 and is connected with an inert gas conduit I61 and has heating element means I68. Screw means I69 is provided in the bottom of the furnace for pressing the investment ring 21' firmly against the door I 62. The investment ring 21' in this instance does not have any notches in the ends thereof.

The furnace I56 is turned into an upright position at right angles from the position shown in Fig. 9 and the door I62 is opened when an investment ring is to be placed in or taken out of the furnace. After a properly conditioned investment ring has been correctly placed in the furnace I 56 and metal, which is to be used in casting, has been placed in the crucible I65, the door I62 is closed against the investment ring with a step portion I 64 of proper size on said door projecting slightly into the end of the investment ring and said door is fastened in closed position by fastening means I10. The furnace I56 and crucible I65 are then angularly moved into the position shown in Fig. 9 and inert gas is As soon as the investment material has been heated to the proper temperature'and the metal reduced to a molten and fluid state, the furnace I56 and crucible I65 are angularly moved back into an upright position, allowing the molten metal to flow by gravity into the mold cavity in the investment material.

Fig. 9 also shows a means for supplying inert gas to the interior of the furnace I56 when the crucible is disconnected therefrom and similar inert gas supply means may be connected with the other furnaces herein disclosed. This inert gas supply means comprises a hose IH connected by readily detachable coupling means I12 with a valve I13 which is connected by a pipe I 14 with a conduit I15 which leads to the interior of the furnace I56. This independent inert gas inlet means to a furnace of this type makes it possible to heat treat metal or metal parts in the investment furnace in the presence of inert gas. Also this independent inert gas inlet makes it possible to solder metal parts together in the furnace in the presence of a flow of inert-gas, thereby eliminating the necessity of using a flux to prevent oxidation and contamination of the metal parts during the soldering process. To facilitate thus using the furnace for soldering it is desirable to provide a table or stand to be used in the furnace to support the parts .to be soldered. Such a table is shown in Fig. 19 and comprises a table top H8 adapted to be supported at different elevations within the furnace by adjustable supporting means. Preferably this supporting means is in the nature of a plurality of interchangeable rings 5?? of different height. By providing bevels H8 on the ends of these rings to interiit each other when the rings are placed end to end I provide a more stable support. Obviously the ends of these rings may be flat or may be shaped differently than shown. A circular groove W9 is provided in the bottom side of the table top to receive the beveled end of the uppermost ring lll. By using more or less rings and different combinations of rings the elevation of the table top may be varied to suit the requirements of the work. When using the furnace for soldering, the parts to be soldered will preferably be placed on the table within the furnace, a cover will be applied to the furnace and the parts brought up to a temperature just sufiicient to melt the solder to be used. Under these conditions the solder will flow very freely and a superior quality of soldering work can be done without using fluxes. sity for electric welding in many instances. The table may be used to support any material to be heat treated or worked on in the furnace.

The electric heating means'in any or all of the crucibles 52, 93, H6, Md, and 565 may employ grooves, like the grooves 25 shown in Figure 1, for the reception of the heating elements. I have shown and described resistance type electric heating means in all of the crucibles herein disclosed, but it will be understood that other types of electric heating means may be employed, as for instance, the well known induction type electric heater may be used instead of the type disclosed in the drawings.

Obviously, changes may be made in the forms, dimensions and arrangement of the parts of my invention, without departing from the principle thereof, the above setting forth only preferred.

forms of embodiment.

I claim:

1. Mechanism of the class described comprising a furnace having a heating receptacle adapted. to receive an investment ring containing investment material, said investment material having a recess extending from the exterior thereof inwardly; and pyrometer means longitudinally movable through a wall of said furnace positioned to extend into the recess in th investment material.

This eliminates the neces- 2. Mechanism of the class described comprising a furnace having a heating receptacle adapted to receive an investment ring containing investment material, said investment material having a recess extending from the exterior thereof inwardly for the reception of pyrometer means; a pyrometer member longitudinally movable through a wall of said furnace positioned to extend into said recess in the investment material; and resilient means urging said pyrometer member into said recess in said investment material.

3. Mechanism. of the class described comprising a furnace; a crucible housing positioned in registration with said furnace when in a casting position, said crucible housing having a crucible chamber provided therein; a cup shaped crucible pivotally mounted in said crucible chamber and movable from a metal holding to a metal discharging position; gas conduit means in said crucible housing directed toward said crucible whereby said crucible may be moved into a. metal discharging position by the inlet of gas through said conduit; and gas pressure supply means connected with said gas conduit means.

4. Mechanism of the class described comprising a furnace having a heating receptacle; a plurality of radial ribs in the bottom portion of said heating receptacle, some of said ribs being relatively offset at angles greater or less than one hundred eighty degrees; and investment ring receptacle, whereby said investment ring means is correctly centered in said heating receptacle.

5. Mechanism of the class described comprising a furnace having a heating receptacle adapted to receive an investment ring containing investment material; a crucible housing having a crucible chamber therein; said furnace and said crucible housing being relatively movable into end to end relation to position the heating chamber and the crucible chamber in registration; a lining member in said crucible chamber supported for movement toward and away from the investment material in said furnace; lining member moving means connected with said lining member; and a crucible pivotally supported in said lining member whereby it may be moved into ceptacle may be positioned in registration with each other; a hollow lining member movably disposed in said crucible chamber for adjustment into sealing engagement with investment material in rings of different size within said furnace, said lining member having a shank extending into said passageway; lining member moving means connected with said shank and a crucible supported in said lining member and movable into a discharging position.

'7. Mechanism of the class described comprising a crucible housing; horizontal pivot means supporting said crucible housing for swinging movement; releasable means positioned to support said crucible housing in a substantially horizontal position; crucible means within said crucible housing having a discharge opening at one end portion of said crucible housing; and a furnace hinged to said crucible housing for swinging movement into and out of axial alignment therewith, said furnace having a heating receptacle adapted to receive an investment material and said furnace being swingingly movable along with said crucible housing.

8. Mechanism of the class described comprising a casting furnace having a receptacle for the reception of a casting investment; a crucible housing connected with said casting furnace and having a crucible chamber communicating with the furnace; means pivotally supporting said crucible housing and said furnace for movement between a substantially horizontal metal melting position and a substantially vertical metal casting position; gas pressure supply means connected with said crucible chamber; and valve means operatively connected with said pivotal supporting means controlling said gas pressure supply means, said valve means being adapted to be opened upon movement of said crucible means into a substantially vertical position, whereby gas under pressure will be admitted to said crucible chamber and said furnace simultaneously with the pouring of the molten metal into the casting investment.

9. Mechanism of the class described comprising a furnace having a heating receptacle adapted to receive an investment ring containing investment material; hinge' means supporting said furnace for angular movement between a position in which the axis of said furnace is substantially horizontal and a position in which the axis of said furnace is substantially vertical; a guide member angularly movable with said furnace and extending substantially parallel to the axis thereof; and a crucible member supported on said guide member for movement toward and away from said furnace and adapted to register with said heating receptacle when in a casting position, whereby molten metal from said crucible member will be discharged into investment material in said heating receptacle when said furnace is angularly moved into 'a' substantially vertical position. 4 10. Mechanism of the class described comprising a furnace having a heating receptacle adapted to receive an investment ring containing investment material; pivot means supporting said furnace for angular movement between a substantially horizontal and a substantially vertical position; a door member hinged to the furnace and movable between an open and a closed position relative to said heating receptacle; and crucible means carried by said door member and having a discharge opening extending through said door member and positioned to discharge molten metal from said crucible into investment'material in said heating receptacle when said furnace is angularly moved into a substantially vertical position. i

11. Dental casting apparatus comprising a closed receptacle; a chamber in said receptacle for receiving therein investment means; heating means for investment means in said chamber; a

metal melting crucible in said receptacle op-' eratively positioned relative to investment means in said chamber; means movably mounting said crucible providing a position for melting metal and aposition for pouring molten metal into said investment means; heating means for said crucible; and externally positioned means controlling the operative position of the crucible relative to said investment means.

12. Dental casting apparatus comprising a closed receptacle; a chamber in said receptacle for receiving therein investment means; heating means for investment means in said chamber; a metal melting crucible in said receptacle operatively positioned relative to investment means in said chamber and having a position for melting and a position for pouring molten metal into said investment means; heating means for said crucible; and pivot means mounting said receptacle and the crucible therein for movement between the melting position and the pouring position of th crucible.

13. Mechanism of the class described comprising an upright furnace having a receptacle for the reception of casting investment means; heating means for said furnace; an upright support positioned at one side of said furnace; a crucible supporting arm longitudinally and rotatably movable on said upright support; and a crucible supported by said supporting arm for angular movement axially of said supporting arm, whereby said crucible may be moved vertically and transversely relative to said furnace and may be moved angularly on said supporting arm to facilitate access to the interior of said crucible.

GEORGE A. YANTIS. 

